Overwintering plants - Relative Humidity

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el48tel
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Overwintering plants - Relative Humidity

Post by el48tel » Thu Dec 06, 2018 3:38 pm

I can maintain 5C in my new greenhouse (yes newbie advice) -- but what should the maximum RH be?
Beginning a new journey of discovery as I grow cactus seeds and offsets for the first time; discover all kinds of wonderful plants in Cactus Nurseries; just love Echinopsis
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Re: Overwintering plants - Relative Humidity

Post by topsy » Thu Dec 06, 2018 3:42 pm

HI,

It depends what plants you grow, how crowded they are and whether you have any fans to move the air around.

Suzanne
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el48tel
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Re: Overwintering plants - Relative Humidity

Post by el48tel » Thu Dec 06, 2018 4:16 pm

topsy wrote:
Thu Dec 06, 2018 3:42 pm
HI,

It depends what plants you grow, how crowded they are and whether you have any fans to move the air around.

Suzanne
Hi Suzanne
It's the cacti such as Echinopsis Gymnocalcium etc which I'll move over.
The sensitive stuff like Schlumbergera will stay in the house
The heater has a fan and is controlled by InkBird ---- and yes I've tested the system and can maintain the temperature
Beginning a new journey of discovery as I grow cactus seeds and offsets for the first time; discover all kinds of wonderful plants in Cactus Nurseries; just love Echinopsis
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Re: Overwintering plants - Relative Humidity

Post by esp » Thu Dec 06, 2018 5:08 pm

Outdoors, RH will often be very high over winter (in the range 93 to 98% where I live today, according to the met office). With an air temperature of 5deg C, it needs very little moisture content in the air (<7g per cubic metre) to get a RH of 100%.

So it may not be realistic to target a low RH, unless you run a dehumidifier - overkill for most people?

A non-porous floor, good weather sealing and a collection of extremely dry plants will help.

Bear in mind that many cacti will be subject to dew in habitat in the winter - although daytime temperatures will often rise a lot (and hence RH fall a lot), as many habitats have a lot more winter sun that the UK.
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Re: Overwintering plants - Relative Humidity

Post by Terry S. » Fri Dec 07, 2018 8:50 am

Just don't worry about the relative humidity. It tends to be at its highest in our greenhouses in late autumn and just watch out at that time for any botrytis that might form on plants. This is unlikely with cacti unless there are recently-dead flowers on them. Certain succulents such as some crassulas and adromischus are susceptible, as are very young seedlings. Many of the other succulents that grow in the western part of South Africa survive on winter fogs as much as actual precipitation and they seem to quite enjoy an environment which is fairly humid at times.
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Re: Overwintering plants - Relative Humidity

Post by juster » Fri Dec 07, 2018 12:31 pm

I think Terry has summarised it well. On fine dry days, unless it's freezing cold, I always go out and open the greenhouse windows to increase ventilation, remembering to shut them later. I even did this when I was working, although it was sometimes more tricky to judge what to do for a whole day. In the end, no gardening is a static process, plants grow and change, sometimes they thrive, sometimes they die. I expect to lose a few plants over the winter and have lost count of the plants I 'used to have'! We can only do our best and enjoy it when they thrive.
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el48tel
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Re: Overwintering plants - Relative Humidity

Post by el48tel » Fri Dec 07, 2018 5:11 pm

thanks guys - my mind is now not so disturbed about this
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Re: Overwintering plants - Relative Humidity

Post by N.D. » Sun Dec 09, 2018 11:18 pm

What is the minimum RH for mesembs that would be OK during winter?

My problem is low humidity. My mesembs are kept indoors over winter. It is way too warm for them indoors (especially once you shine some intense light at them), and I cool them by blowing outside air (at about -15C and 60%RH) onto them. In the process, the outside air warms up to +5...+15C. This brings RH down to about 10%. That's dry. Some plants shrivel pretty quickly, and I am not sure what to do about this. Watering many mesembs during winter is a bad idea.
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Re: Overwintering plants - Relative Humidity

Post by ralphrmartin » Mon Dec 10, 2018 11:59 am

My plants are doing just fine in conditions where the RH can go up to 100% after rain, or as the temperature drops.

However, I do have fans which come on when the RH is over 90%, to try to help prevent botrytis etc.
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Re: Overwintering plants - Relative Humidity

Post by el48tel » Mon Dec 10, 2018 2:06 pm

N.D. wrote:
Sun Dec 09, 2018 11:18 pm
What is the minimum RH for mesembs that would be OK during winter?

My problem is low humidity. My mesembs are kept indoors over winter. It is way too warm for them indoors (especially once you shine some intense light at them), and I cool them by blowing outside air (at about -15C and 60%RH) onto them. In the process, the outside air warms up to +5...+15C. This brings RH down to about 10%. That's dry. Some plants shrivel pretty quickly, and I am not sure what to do about this. Watering many mesembs during winter is a bad idea.
Have you considered putting open bowls or tall containers of water interspersed between the plants to raise the RH?
Beginning a new journey of discovery as I grow cactus seeds and offsets for the first time; discover all kinds of wonderful plants in Cactus Nurseries; just love Echinopsis
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